IIRC the recommended rpm for that engine is 5250-5750. Running 5000 is a little low. Going from alum to ss should bring it up a little, but there's a lot more to it than just prop pitch. If the engine is mounted too low that can also reduce rpm because of more drag and also causing considerable speed and fuel efficiency loss. If you don't want to mess with what you have now, then a 16p prop should bring the rpm close to in the recommended rpm range. Personally, I'd pull the intake air restrictor out to increase power of the engine and stay with the same pitch or maybe go up in pitch if the rpms max out.